It is unclear to me exactly what EPR are trying to represent?
Is an EPR a reference to an "endpoint" or a service? If so, WSDL 2.0
defines an Endpoint as well. This Endpoint is not very different from
wsdl11:port. What is the relationship between a WSDL Endpoint and an EPR?
An EPR allows, in fact, to include (optionally) a service endpoint/port.
If such an endpoint/port is included in an EPR, what is the relationship
between the value of the [address] property and the URI value in the
[service-port] property?
At the very least the use of the term 'endpoint' in WS-A is confusing
because of the use of the same term in WSDL.
The WS-Addressing submission, section 2 [1] does say some about this:
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...
Because of the current limits of the WSDL 1.1 extensibility model, the
WSDL 1.1 service and port elements cannot be used to cover the use cases
listed above. Endpoint references logically extend the WSDL description
model (e.g., portTypes, bindings, etc.), but do not replace it. Endpoint
references will be used instead of WSDL <service/> elements in the
following cases:
* Specific instances of a stateful service need to be identified or
its instance-specific configuration details need to be transmitted.
* A lightweight, self-contained description of a service endpoint
needs to be communicated. In particular, this may be necessary when the
details of the endpoint configuration are already shared by the
communicating parties, but specific policy information needs to be added
or updated, typically as a result of a dynamic configuration process.
Endpoint references complement and do not replace the WSDL/1.1
<wsdl:service> element. We expect solutions built on WSDL/1.1 to
continue to utilize a service element. Moving forward we anticipate that
endpoint references and WSDL will evolve coherently. The endpoint
references may link to service elements in WSDL/1.1, and support
additional scenarios in which the WSDL information is not known by a
party processing a message. These scenarios may include dynamic
messaging or limited capability message processors.
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WSDL 2.0 certainly has the extensibility that WS-Addressing needs. Wrt
to WSDL 1.1, Service/port elements are extensible via elements as well
as attributes. In face WS-I Basic Profile 1.1 [2] makes all the elements
in the WSDL 1.1 namespace extensible via elements as well as attributes.
So I don't see how WSDL extensibility comes in the way of reusing WSDL
elements in WS-Addressing.
EPR is essentially a service reference. I would like to understand the
constraints/requirements that led to the creation of additional
syntactic structures rather than the reuse of existing structure.
Specifically, I would like to understand why the wsdl service element
cannot be used here instead of wsa:EndpointReference ?
-Anish
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[1]
http://www.w3.org/Submission/2004/SUBM-ws-addressing-20040810/#_Toc77464317
[2]
http://www.ws-i.org/Profiles/BasicProfile-1.1-2004-08-24.html#WSDL_Extensions